At least I will much more often be with a phone with no WiFi access than within WiFi access with no computing device except a phone. And if I have something other than a phone available, I'm really not going to use Skype on the phone. The old Linux version of Skype wasn't the most brilliant piece of software ever, but even it is so far ahead of the phone versions of Skype that it's not even funny.
Does Skype run decently on any phone platform? I know the Android version will drain the battery dry faster than playing a 3D game and will not reliably receive calls even when running in the foreground. And it's my understanding that the WP7 version requires so much memory it doesn't even run on all WP7 phones, and will not run at all in the background making it totally useless.
At this point the idea that Skype + mobile would be some kind of a killer combination worth billions seems like a total pipe-dream. The only real-world effect it has is to kill Nokia faster due to mobile operators hating Skype, and not wanting to be aligned with MS.